1. Field of the Invention
The invention concerns the processing of Group III-V compound semiconductor devices by etching.
2. Description of the Prior Art
Techniques for the processing of Group III-V semiconductor materials are currently under intensive development. One area of development is the provision of etchants which will not destroy the gold contact areas, which are present on the semiconductor wafer during the later processing steps in device fabrication, while rapidly and smoothly etching the semiconductor material. Etchants in general use in Group III-V compound semiconductor processing technology are less than optimum for this use in one or another respect. For instance, aqua regia or bromine-in-methanol, which etch Group III-V materials relatively rapidly, also attack the gold contacts or areas of the wafer protected by oxide layers. Other etchants compatible with the gold contacts, such as H.sub.2 SO.sub.4 :H.sub.2 O.sub.2, etch the semiconductor material at a rate which is too slow for many purposes especially in the widely used but difficultly etched metal-(111) direction (i.e. the (111) face containing the Group III constituent).
An etchant, which has been used in the investigation of dislocations in bare wafers of the Group III-V compound semiconductors by producing etch pits on (111) faces, is a solution containing approximately 0.25 molar K.sub.3 Fe(CN).sub.6 and approximately 2 molar KOH (Soviet Physical: Solid State, Vol. 8 [1967] page 1976). Such etch pits generally become deeper as etching proceeds. A similar composition has been used simultaneously with mechanical polishing to produce smooth surfaces on wafers of the subject materials (German Patent No. 1,227,307 issued Oct. 20, 1966, to Siemens and Halske A.-G.). However, such simultaneously processing cannot be used when contacts or passivation layers are present on the wafer surfaces to be etched.